This image shows a hill with a central crater. Such features have been interpreted as both mud volcanoes (really a sedimentary structure) and as actual volcanoes (the erupting lava kind). They occur on the floor of Valles Marineris below a closed topographic contour that could have held a lake, and the compaction of wet sediments may have created mud volcanoes.

The fracture pattern of the bright flow unit surrounding the hill resembles mud cracks. However, there have also been observations from the CRISM instrument interpreted as high-temperature minerals, suggesting actual volcanism, although not necessarily at this location. Fine layers in the hill are consistent with either volcanism or mud flows.

Either way, this activity is relatively recent in geologic time and may mark habitable subsurface environments.

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POSTSCRIPT
NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance
Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.